The present invention relates to metrology, more particularly to utilization of retroreflective targets for effecting laser tracking.
“Metrology” is a broad term referring to the science and study of weights and measures and measurement. Three-dimensional geometries of objects are often measured using a coordinate measuring machine (CMM), which displays readings received from one or more probes. Numerous industries require precise measurements of three-dimensional shapes.
A kind of CMM known as a laser tracker is prevalent in military and industry. According to typical operation of a laser tracker, a retroreflective target is maintained in contact with an object. An oft-used type of retroreflective target is a spherically mounted retroreflector (SMR). A laser beam is emitted by the laser tracker and impinges upon the SMR, which reflects laser light back to the laser tracker along the original path from the laser tracker. The laser tracker includes an interferometer, which measures the distance from the laser tracker to the SMR based on laser light that re-enters the laser tracker. The laser beam is thus tracked by the laser tracker so as to measure mathematical/spatial coordinates (e.g. distance and two angles) that correspond to the location of the SMR.
A conventional approach to performing laser tracking with respect to a hollow cylindrical object involves placement of a spring-loaded touch probe to determine depth at a single point. The spring-loaded touch probe is then removed to record the data taken and is subsequently set up again, further down the bore of the object, for another measurement. Conventional methods, such as those implementing feeler gauges and micrometers, tend to be slow, tedious, inaccurate, and difficult to repeat without variances.